1. Field of the Invention
The present invention relates to a pyrotechnic charge, in particular a pyrotechnic charge for producing IR radiation, which can advantageously be used in an infrared decoy.
In the military sector, missiles, such as air-to-air and ground-to-air guided missiles, which head for and pursue the infrared (IR) radiation emitted by the engine of the target, chiefly in the range between 0.8 and 5 μm, with the aid of a search head sensitive to IR radiation, are used for combatting air targets, such as, for example, jet aircraft, helicopters and transport machines. For defence against these missiles, decoys (also referred to as flares) which imitate the IR signature of the target in order to deflect approaching guided missiles are therefore used. Such decoys can also be used preventively in order to complicate or even prevent the detection of targets by reducing the contrast of the scene.
A typical active composition for producing black body radiation in the IR range is a pyrotechnic charge comprising magnesium, polytetrafluoroethylene (Teflon®) and vinylidene fluoride/hexafluoroisoprene copolymer (Viton®), also referred to as MTV, which exhibits a black body-like spectral intensity distribution on combustion. However, the actual signature of, for example, aircraft engines differs from the signature of a black body emitter since the hot exhaust gases of the turboprop or jet engines emit strong selective components in the wavelength range between 3 and 5 μm (so-called β-band). This selective radiant emission is due to the combustion products CO and CO2, which emit at 4.61 μm and 4.17 μm, respectively.
2. Discussion of the Prior Art
In order to distinguish between decoys having a black body signature and genuine flying targets, modern homing heads therefore additionally carry out a spectral evaluation of the radiation. Particular attention is paid to the fact that the integrated intensity of the signature of an aircraft or its engine in the wavelength range between 3 and 5 μm (β-band) is a factor of 2 greater than the integrated intensity in the wavelength range between 2 and 3 μm (so-called α-band). In the case of decoys having a black body signature, this ratio is, on the other hand, always less than 1.
In order to overcome the spectral differentiation of decoys by homing heads on this basis, adapted decoys which have an aircraft-like spectral intensity distribution were proposed in the past.
For example, decoys which contain pyrotechnic charges based on carbon-rich compounds and oxygen carriers are being proposed for this purpose. In addition, those active charges which contain boron as a fuel were also proposed. The combustion of carbon-rich compounds results in the formation of, in particular, CO and CO2, which serve for the selective radiation emission in the β-band from 3 to 5 μm; the combustion of boron results in particular in the formation of HBO and HOBO, which likewise selectively emit in the β-band at 3.51 and at 4.94 μm and 2.72 μm, respectively.
In the design of the first-mentioned, carbon-rich active charges, it is necessary to achieve in the case of the combustion products a CO2/H2O ratio which is always substantially less than 1. This is associated with the selective radiant emission of water in the wavelength range at 2.73 μm. The excessive formation of water should therefore be avoided as far as possible with regard to the quotient of the integrated intensities in the α-band and β-band, explained above. For this reason, the prior art proposed, for example, hydrogen-poor aromatic carboxylic anhydrides (cf. U.S. Pat. No. 6,427,599) and hydrogen-rich cyano compounds as fuels in pyrotechnic active compositions for spectrally adapted decoys. However, the hydrogen contained in the carbon-containing compositions always also leads to strong radiant emissions in the α-band, due to substances such as HO (2.67 μm), HCl (3.34 μm) and H2O (2.73 μm).
With the use of boron as fuel, the hydrogen present from, for example, the ammonium perchlorate, likewise always leads to an impairment of the spectral ratio since HOBO formed in the flame also emits at 2.72 μm and therefore contributes to an increase in the integrated intensity in the range from 2 to 3 μm (α-band).
In the case of said conventional active compositions, the radiant emission in these wavelength ranges therefore reduces the efficiency of the respective decoys on the one hand due to false components in the short-wave α-band, which in the worst case lead to rejection of the decoy, and, on the other hand, due to an only slightly specific radiant emission in the β-band in the acquisition range of the decoy.